Dialog Merging - What is this exactly? This deals with merging in lines of dialog from mods with vanilla dialog?

Affects the expansions and mods. Each ESM and ESP file can define new dialog responses for a given topic. Dialog topics contain a linked list of responses, where responses at the beginning of the list have priority of being chosen. This means the order of the list is crucial for gameplay. When several game files modify the same dialog topic then their lists must be merged into one, carefully keeping the order intact. In previous versions, we simply added new dialogue lines to the end of the list, which caused dialog responses added by plugins to almost never appear.

Missing Creature State - What exactly were we missing? It looks like this means we keep better track of spells now? (for the player and NPCs/Creatures?)

In 0.30 save state was missing for known spells, active spell effects, AI packages, AI settings, summoned creatures, and some minor stuff.

All essential game state should now be included in save games. If you find something that isn't, raise a bug. Note this does not include actor animation state (issue #1225).

Leveled Creature Handling - Okay, so duplicate creatures don't spawn on top of each other now. Why did they in the first place?

A levelled creature reference will spawn a creature if it hasn't spawned one yet. Due to the spawning state not being in the save game, it would "forget" that it already spawned a creature, and spawn another.

If anyone's interested, 0.31.0 is stable so far and very smooth on my machine when built with the following flags and g++ 4.9.1 on Linux. Framerate is lowish still but that's expected: these optimizations apply to CPU-bound tasks and not 3D acceleration.

And CPU-specific flags that may not work for you. Check /proc/cpuinfo for supported features. pni (prescott new instructions: sse3), cx16, abm, and similar. Run dmidecode as root to find L1 and L2 cache sizes in kilobytes (gcc by default uses small sizes, 128 and 1024 here).

Okay so here's some very belated commentary on v0.31.0. It's not as thorough or polished as I'd like, but it's what I can offer.
It's unlisted now. Someone give it a look-see for glaring inaccuracies/mistakes?